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When I am running an interactive bash session, I sometimes experiment with sh.

I call sh directly from this bash session.

My question is, how can I change the PS1 prompt of this subshell?

I would like the prompt to be something like sh$, notifying me that I am using sh and not bash.

What I have tried so far is:

  • I made a configuration file analogous to .bashrc named .shrc
  • I put only one line in it: export PS1='$(echo ${0})\$ '

  • I then modified ~/.profile to say the following:

    # if running bash
if [ -n "$BASH_VERSION" ]; then
# include .bashrc if it exists
    if [ -f "$HOME/.bashrc" ]; then
        . "$HOME/.bashrc"
    fi
# if running another shell
else
    if [ -f "$HOME/.shrc" ]; then
        . "$HOME/.shrc"
    fi
fi

  • I restarted the terminal, but the changes are not being applied.

  • If I run . ~/.shrc in sh manually, the changes do get applied.

What am I doing wrong?

Stefan van den Akker
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1 Answers1

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It won't source that file by default. You can direct it to do so:

ENV=~/.shrc sh

Or you might add:

alias sh="PS1='\$0\$ ' sh"

To your usual shell's environment file. It could simplify things.

Or even:

alias sh='ENV=~/.shrc sh'

Still, if you only want to declare the one variable for it, explicitly setting $PS1 on the command line like in the first alias example is probably the better way to go.

mikeserv
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  • Nice solutions! What is going on with all the single apostrophes in `alias sh='PS1='\''$0\$ '\'' sh'`? – Stefan van den Akker Jul 30 '14 at 11:57
  • @Netfas - You can't put a hard quote within a hard-quoted string, but you can quote a hard quote though like `"'"` or `\'`. So what those do is close the current string like `'current string'` wedges a backslash quoted hard quote in like `\'` then starts a new one like `'next string'` - and they all get concatenated. `'string'\''string'` – mikeserv Jul 30 '14 at 12:00
  • And we need the hard quotes to prevent premature expansion of the `$0\$` part (`alias sh="PS1='$0\$ ' sh"` results in `bash$`), right? – Stefan van den Akker Jul 30 '14 at 12:08
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    @Netfas - right `$PS1` is special - it is `eval`ed at each prompt. So you need the shell script in there, not the expansion of the variables. Especially since when you call it on the command line, it isn't even `$0` yet - that's still `bash` at that time. If you do `alias sh="PS1'$0\$ ' sh"` - you're quoting the hardquotes - and `$0` is expanded. But this would work: `alias sh="PS1='\$0\$ ' sh"`. – mikeserv Jul 30 '14 at 12:12
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    @Netfas - actually, on second thought that's wrong - it's not about when you call it on the command line, it's about protecting `$0` at `alias` definition time. Sorry about that. Anyway, the command still works, I just got ahead of myself I guess. And by the way, [this](http://unix.stackexchange.com/a/124904/52934) makes for a pretty handy prompt in `sh` mode. – mikeserv Jul 30 '14 at 12:23
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    Awesome! I am definitely going to try that :) – Stefan van den Akker Jul 30 '14 at 12:32
  • One thing is still bothering me: what configuration file for `sh` is being read when you you call a subshell in `bash`? I mean, the subshell has a default `PS1` of `$`, where does that come from? Where is that default defined? – Stefan van den Akker Jul 30 '14 at 13:14
  • @Netfas - In the executable - it's compiled in behavior... or maybe it's set in the link. `sh` is just a link to `bash` run like `bash --posix --norc --noprofile`. At least I think that makes all of it. You're not actually running a program all its own. – mikeserv Jul 30 '14 at 17:19